1. Field of the Invention
The present invention relates to weighing scales, and more particularly to portable scales that resemble cargo pallets mounted to pallet trucks and that can accurately weigh loads of several thousand pounds.
2. Description of Related Art
Trucking and other shipping companies often charge their customers according to the weight of shipments. So it is important to both the shipper and customer that the weight of a shipment be accurately determined at convenient places.
Typical cargo units are loaded onto trucks using forklifts because they can weigh as much as 5,000 pounds. A scale strong enough and accurate enough to weigh such forklift pallet loads can weigh 200 to 400 pounds itself. So moving such a scale around a loading dock or out to a customer pickup location is very awkward and difficult.
A platform weighing scale is described by Herbert Wagner, et al., in U.S. Pat. No., 3,935,913, issued Feb. 3, 1976. Such platform weighing scale has a reinforced load cell-supported platform with a frame-like reinforcement. A load-receiving deck or platform is used to define a torsion box frame which resists load-induced deflection of the platform between the load-cell support points. Low profile platform scales for weighing relatively heavy loads are short in overall height, as measured from the floor or other scale-support surface to the top of the load-receiving platform or deck. Scales of this type are especially suitable for weighing loads which are carted by such vehicles as tote bins, push carts, dollies, fork lift trucks and other usually relatively small motor vehicles. Conventional low-profile type platform scales normally do not require installation in a pit to accommodate load-carrying vehicles and roll-on loads in general because the platform is relatively close to the floor surface and can easily be accessed by relatively short, gently sloped ramps. Herbert Wagner, et al., observed that low profile type platform scales offer an advantage of not needing to be installed in a pit. On the other hand, in installations where it is desired to locate the platform flush with the floor surface, only a shallow pit is needed.
U.S. Pat. No., 3,587,761 issued Jun. 28, 1971 to L. C. Merriam, et al., uses a special structure interposed between each load cell and the platform to avoid side loading of the cells. Such patent illustrates a typical platform structure having a deck plate and reinforcing beams which are seated on the platform-supporting load cells. Other examples of prior weighing scales are shown in U.S. Pat. No., 3,103,984, which issued to C. L. Ellis, et al., on Sep. 17, 1963; U.S. Pat. No., 2,962,276, which issued to A. L. Thurston on Nov. 29, 1960; U.S. Pat. No., 3,679,011, which issued to I. M. Hawver on Jul. 25, 1972; and, U.S. Pat. No., 3,565,196, which issued to E. Laimins on Feb. 23, 1971.
The prior art has discussed the ill-effects of side loading forces applied to load cells. Such side loading can adversely effect accuracy, and some can permanently damage the load cell. A few researchers have proposed solutions, e.g., U.S. Pat. No. 4,611,677, issued Sep. 16, 1986, titled, Shock Proof Scale; U.S. Pat. No. 4,305,475, issued Dec. 15, 1981 titled, Weigh Block Assembly; U.S. Pat. No. 4,453,607, issued Jun. 12, 1984, titled, Weight Scale With Side Load Protection; U.S. Pat. No. 4,601,356, issued Jul. 22, 1986, titled, Suspended Platform Scale Structure; and, U.S. Pat. No. 4,248,317, issued Feb. 3, 1981 titled, Load Cell Apparatus